High-field paramagnetic Meissner effect and flux creep in low-T_cTi–V alloy superconductors

Abstract

We report an experimental study on the high-field paramagnetic Meissner effect (HFPME) performed by measuring both the temperature and time dependence of magnetization in the two compositions of superconducting Ti–V alloys where certain secondary phases are non-superconducting, and thereby act as efficient pinning centres for the flux lines. While spatially non-uniform flux density driven by flux line pinning at these secondary phases is the necessary condition for the observation of the HFPME, our study indicates that the flux creep effect plays a supplementary role to reinforce the HFPME. It is found that in the temperature and magnetic field regime of the HFPME, the field-cooled magnetization of these samples relaxes monotonically towards a more positive value with elapsed time. We comment on how this paramagnetic relaxation behaviour of the field-cooled magnetization is correlated with the unusual thermo-magnetic responses related to the HFPME.

Strong paramagnetic response in the superconducting state of Y-containing V0.6Ti0.4 alloys

“…in these alloys include: (a) negative temperature coefficient of resistivity [3], (b) the presence of itinerant spin fluctuations [3][4][5] and (c) phonon-dominated heat conduction in the superconducting state [6]. Recently, the presence of a high-field paramagnetic Meissner effect (HFPME) was reported in a few V-Ti alloys in the field range 0.05-1.5 T [7,8].…”

“…However, in a few superconductors, such as Mo-Re [11], YBa 2 Cu 3 O 7−δ [12][13][14], Nb thin films [15] and a few V-Ti alloys, the magnetisation in the FCW experiments is greater than in the FCC experiments [7,8]. Such behaviour is seen in the mixed superconducting state and is known as the HFPME.…”

“…In some cases, the paramagnetic response is so large that the field-cooled (FC) magnetisation is higher than the normalstate magnetisation [15,16]. Relaxation of FC magnetisation towards more positive values is also a characteristic feature of the HFPME [7,12,15]. Inhomogeneous flux line pinning inside the sample is the reason behind the observation of the HFPME in the mixed state [7,8].…”

Microstructure and substrate dependent enhanced critical current density in Pb-substituted Bi-based high temperature superconducting thin films

“…While the real part (χ′) of AC susceptibility represents the transition from the normal to the completely superconducting state, its imaginary part (χ″) exhibits a peak which is the measure of dissipation in the sample due to weak links [11]. The weak links like secondary phases found near the grain boundaries formed between the grains largely influence the J C behaviour [8,12]. A very large J C can be achieved in a tunneling junction where the weak links are metallic [13].…”

“…PME was first observed in Bi-based HTSC [19]. Subsequently, this phenomenon was found to be inherent in many other compounds like YBa 2 Cu 3 O 7−δ , Nb, Ti-V alloys, La 1.85 Sr 0.15 CuO 4 , RbEuFe 4 As 4, etc [12,16,[20][21][22][23][24][25]. However, such studies of PME in the thin film samples are less explored [16,20,26].…”